Such a suction head is usually disposed vertically and has an upwardly extending slag suction path formed therewithin, with a lower end suction port positioned close above the slag. Nozzles for spraying cooling water toward the slag suction path are disposed around the lower end suction port, so that the slag, as it is sucked, is cooled by the cooling water from the nozzles and is thus solidified. The suction head is of a duplex tube construction such that its inner tube defines the slag suction path, with a gap defined between the inner tube and an outer tube, the gap being utilized as a cooling water down-flow passage for supply of cooling water to the nozzles.
Conventionally, means for stopping and resuming water feed to the nozzles comprise a shutter for opening and closing the nozzles, and a drive mechanism for opening and closing the shutter by air pressure. The shutter comprises a cylindrical member disposed adjacent an outer peripheral portion of the inner tube, and is adapted to be moved back and forth by the drive mechanism in the axial direction so that it is opened and closed.
Since it is disposed adjacent the inner tube defining the slag suction path, however, the shutter is subject to thermal deformation by the hot slag passing through the slag suction path. Such thermal deformation may often render it impossible to open and close the nozzles.